Such industrial measuring systems, which are implemented for coordinate position determination of points on a surface, and are formed by a handheld measuring aid in cooperation with a station which surveys the measuring aid in space—such as a six-degrees-of-freedom laser tracker in particular—have been known for some time from the prior art.
Examples of such systems are described, for example, in the patent literature publications WO 1993/07443 A1, WO 1997/14015 A1, WO 2007/124009 A2, or WO 2007/124010 A2, or are also known in the form of the products laser tracker “AT901” and measuring aid “T probe”, sold by Leica Geosystems AG.
Such a handheld measuring aid instrument has for this purpose a measuring probe for the object surface, which is arranged on a body of the measuring aid, in particular having a tactile ball to be used for physically contacting a measuring point on the object surface (wherein here notches, holes, concealed points, etc. are also to be understood to form part of the measured object surface of a measured object throughout). Furthermore, visual markings are provided, which are arranged, forming a pattern, on the body in a defined spatial relationship to one another and in relation to the measuring probe in a marking region.
The visual markings can be provided in particular in this case by passive or active light spots, which can be acquired by a camera, in particular wherein the markings are formed by reflectors or by LEDs (light-emitting diodes).
The measuring stations (such as laser trackers in particular) to be used together with the measuring aids can then be embodied, to acquire these markings, having an optical image acquisition unit having a two-dimensional, light-sensitive array, for example, a CCD or CID camera or a camera based on a CMOS array (or having another pixel array sensor) and having an image processing unit. The camera can be installed in this case in particular on the station in such a manner that the positions thereof in relation to one another are not variable. For example, the camera is installed on the station in such a manner that it is pivotable by a motor about one or about two axes and therefore can also track the measuring aid during movement, so that it remains in the region of vision of the camera.
A special example of such measuring stations is represented by the laser tracker with camera. A target point, which can be finely targeted and tracked, for such a laser tracker is formed in this case by a retroreflective unit (for example, a cube prism or corner cube retroreflector), which is targeted using an optical laser measuring beam of the measuring device. The laser beam is reflected by the retroreflector in parallel back to the measuring device, wherein the reflected beam is acquired using an acquisition unit of the device. In this case, an emission or reception direction of the beam is ascertained, for example, by means of sensors for angle measurement, which are associated with a deflection mirror or a targeting unit of the system. In addition, with the acquisition of the beam, a distance from the measuring device to the retroreflector is ascertained, for example, by interferometry or by means of runtime and/or phase difference measurement.
For the cooperation of a measuring aid with a laser tracker, the measuring aid generally has a retroreflector at a central point of its marking region, which can be targeted, tracked, and surveyed in position in three dimensions automatically with high precision by the laser tracker.
For this purpose, laser trackers according to the prior art generally have a tracking surface sensor in the form of a position-sensitive surface detector (for example, a PSD or a CCD or CMOS sensor), wherein measuring laser radiation reflected on the target can be detected thereon and a corresponding output signal can be generated. By means of a downstream or integrated electronic system, the output signal can be analyzed and a focal point can be ascertained, for example. By means of this tracking and fine targeting sensor, a divergence of the point of incidence (focal point) of the acquired beam from a servo-control zero point can thus be determined and, on the basis of the divergence, precise targeting or—in the event of movement—tracking of the laser beam on the retroreflector can be performed. An acquisition using the tracking and fine targeting sensor is performed coaxially to the measuring axis, so that the acquisition direction corresponds to the measuring direction. The application of the tracking and the fine targeting can first be performed after the measuring laser has been aligned at least coarsely on a retroreflective target, in such a manner that the measuring laser beam is incident on the retroreflector (considered at least somewhere in the beam cross section of the measuring laser beam). After more precise targeting, angle and distance measurement is performed—as described above—for the actual surveying of the retroreflector.
The further three degrees of freedom of the measuring aid are determined by recording an image of the markings and corresponding image processing. The unit which guides the laser beam and the camera can in this case be formed in particular in such a manner that their positions in relation to one another are not variable. For example, the camera is rotatable together with the unit about an essentially perpendicular axis, but is pivotable up-and-down independently from the guiding unit and is therefore arranged separately from the optic of the laser beam in particular. Alternatively, the camera can also be embodied as only pivotable about one axis. Furthermore, however, the camera can also alternatively be installed in an integrated construction together with the beam-guiding unit in a rotatable and pivotable shared housing.
Using the acquisition and analysis of the image—by means of image acquisition and image processing units—of the visual markings, the relative location of which to one another is known, the orientation of the measuring aid instrument in space can thus be concluded. Together with the determined spatial position of the retroreflector, the position and orientation of the measuring aid in space can therefore be precisely determined absolutely (or at least in relation to the laser tracker)—and therefore finally the surface point, which is contacted in a tactile or optical manner by the probe of the measuring aid instrument.
Alternatively to the use of a laser tracker as a surveying station for the measuring aid, the station can also be designed in such a manner that six-degrees-of-freedom surveying of the measuring aid can also be performed in a solely camera-based manner, as is described in the above-mentioned patent literature publications WO 2007/124009 A2 or WO 2007/124010 A2.
The measuring aid instrument can furthermore also be, in a way known to a person skilled in the art, a handheld scanner, which is equipped for short-range measurement, for contactless surface surveying, wherein the direction and position of the scanner measuring beam used for the short-range measurement are precisely known in relation to the light spots and reflectors, which are arranged on the scanner. Such a scanner is described, for example, in EP 0 553 266 or also is known in the form of the product “T-Scan”, sold by Leica Geosystems AG.
Measuring aid instruments held in one hand which are known in the prior art are constructed as two-sided in this case, having a front side to be aligned toward the measuring station, on which the visual markings (and also optionally the retroreflector) are arranged in the marking region—all pointing in a joint direction (→ pointing perpendicularly away from the front side)—and a rear side, on which a grip handle to be gripped in an enclosing manner like a rod by a hand (also called a first grip) of a user is arranged.
For some requirements (for example, for special measuring tasks), the first grip (the encompassing grip like a rod of such a handle) can also cause disadvantages, however.